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Hot spot Scientists have found evidence of volcanoes on the far side of the Moon.

The new discovery, reported in the journal Nature Geoscience is a rare example of volcanism on the lunar surface not associated with asteroid, meteor or comet impact events.

Until now the best known examples of volcanism were on the Moon's near side in a region known as the Procellarum KREEP terrane.

A team of scientists, led by Dr Bradley Jolliff from Washington University in St Louis, used images and other data gathered by NASA's Lunar Reconnaissance Orbiter (LRO) to assess the composition of an unusual region on the far side of the moon called the Compton-Belkovich thorium anomaly.

They focused on an area containing numerous domes, some more than six kilometres high.

The domes featured steeply sloping sides which Jolliff and colleagues interpret as, "volcanic in origin and formed from viscous lava".

"We also observe circular depressions, which we suggest result from caldera collapse or volcanic vents," the researchers write.

The LRO data indicates the rocks are rich in thorium, silica and alkali-feldspar minerals, making them different from the black basalts that make up the lunar mare on the near side.

Rare and unusual

Dr Sarah Maddison, an associate professor of Astrophysics at Swinburne University in Melbourne says such a localised region of volcanism on the lunar far side is unusual.

"Most of the volcanism we see on the Moon is impact related and on the near side, although we don't know why," says Maddison.

"But if it's caused by radioactive decay, then why is it limited to the one hot spot and why did it happen so much later than everywhere else on the Moon?"

"It's much higher in silicon and potassium than the basaltic volcanism seen elsewhere on the Moon" says Graham.

"It's also the first evidence of such young volcanic activity on the lunar surface, meaning the Moon was still geologically active just 800 million years ago, rather than 1.2 billion years ago as previously thought."

Graham says, "It's been 42 years this month since we first walked on the Moon and we're still finding out new things".

"It shows there's certainly good scientific justification to send people back there."